<h2>DESCRIPTION</h2>

<em>r.buildvrt</em> builds a virtual raster (VRT) that is a mosaic of 
the list of input raster maps. The purpose of such a VRT is to provide 
fast access to small subsets of the VRT, also with multiple simultaneous 
read requests.

<h2>NOTES</h2>

<em>r.buildvrt</em> creates a list of raster maps that can be 
located in different mapsets. The output is a read-only link to 
the original raster maps which is only valid if the original raster 
maps remain in the originally indicated mapset. A VRT can also be built 
from raster maps registered with <em><a href="r.external.html">r.external</a></em>.

<p>
Reading the whole VRT is slower than reading the equivalent single 
raster map. Only reading small parts of the VRT provides a performance 
benefit.

<p>
A GRASS virtual raster can be regarded as a simplified version of GDAL's 
<a href="http://gdal.org/gdal_vrttut.html">virtual raster format</a>. 
The GRASS equivalent is simpler because issues like nodata, projection, 
resolution, resampling, masking are already handled by native GRASS 
raster routines.

<h2>EXAMPLES</h2>

<h3>VRT from a DEM in the North Carolina sample dataset</h3>

In this exercise a low resolution DEM is resampled to a high
resolution DEM. This is subsequently cut into small tiles and
from that a virtual tile mosaik is created:

<div class="code"><pre>
# set the computational region to elevation map
g.region raster=elev_state_500m -p
# enforce higher resolution
g.region res=50 -p
# resample the 500 meter DEM to 50 meter resolution
r.resamp.interp input=elev_state_500m output=elev_state_50m method=bilinear
# create tiles from resulting large 50 m elevation map
r.tile input=elev_state_50m output=elev_state_50m_tile_ width=1000 height=1000 overlap=0
# for convenience, dump list of tile names to a file
g.list type=raster pattern=elev_state_50m_tile_* output=tilelist.csv
# build a mosaik as VRT from tile list
r.buildvrt file=tilelist.csv output=elev_state_50m_vrt
</pre></div>

<h2>SEE ALSO</h2>

<em>
<a href="r.tile.html">r.tile</a>,
<a href="r.patch.html">r.patch</a>,
<a href="r.external.html">r.external</a>
</em>

<p>
The equivalent GDAL utility 
<em>
<a href="http://gdal.org/gdalbuildvrt.html">gdalbuildvrt</a>
</em>

<h2>AUTHOR</h2>

Markus Metz<br>
Sponsored by <a href="https://www.mundialis.de">mundialis</a>

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